The present invention relates to an arrangement for measuring a fluid pressure. In particular, the invention relates to pressure sensors, which are disposed directly in a hydraulic system and/or a hydraulic control unit of a vehicle brake system.
From working practice it is known to fit pressure sensors into a bore or recess in a hydraulic control unit, which comprises, among other things, valve arrangements, in that the pressure sensors have an external thread, which is screwed into a corresponding internal thread provided in the bore or recess. Such a procedure is costly in terms of manufacture, involves assembly time and moreover does not allow electrical and mechanical connection of the pressure sensor directly to a control circuit on a printed circuit board, which is attached to the hydraulic control unit.
As an alternative to the prior art, it is also known to latch the pressure sensor into the bore or recess in that a spring washer, snap ring or the like is biased in an annular groove disposed at the outer periphery of the pressure sensor and latches into a corresponding annular groove of a diametrically opposed shape in the bore or recess as soon as the pressure sensor is inserted deeply enough into the bore or recess. On the one hand, disassembly for servicing purposes is very difficult because the snap ring has to be dimensioned so as to be capable of withstanding high pressure forces of several tens of bars (60 to 120 bar). On the other hand, a mounting of the pressure sensor in the bore or recess which is free of play in the mounting direction may be realised by means of a snap ring only with difficulty. This would, however, be necessary in order to prevent the transfer of tensile or thrust loads of the pressure sensor to the printed circuit board that carries the control circuit.
Even when the pressure sensor is connected by a plug-in connector or plug-in contact to the printed circuit board, axial displacements of more than 50 xcexcm during operation may lead to the contact resistance increasing to several ohms and hence to a considerable corruption of the measured fluid pressure or even to failure of the plug-in connector and/or pressure sensor.
DE-GM 1 879 755 describes a measuring range transfer apparatus for measuring liquid or gas pressures, in which a cylindrical control slide valve is axially displaceable in a housing. At one axial end of the housing medium is supplied to a pressure chamber and directed towards radial bores in the housing. Control slots are formed in the control slide valve and in a specific position of the control slide valve connect one of the bores to a manometer. Axially opposite surfaces of the control slots are designed to be of equal size. The objective is, as the pressure rises or drops, to disconnect or connect one manometer after the other.
From DE 40 12 619 A1 a mobile device for locating leaks in drains is known, which comprises two double walls for sealing off a pressure chamber. The pressure chamber is filled through an axial supply line with water, the pressure drop of which is measured to determine the leakage point. The device is moved progressively through the drain.
Proceeding from the previously described prior art, the object of the invention is to provide an arrangement for measuring a fluid pressure, which allows easy assembly, or disassembly, in a minimal amount of time and which during operation does not cause any tensile or thrust loads upon a plug-in connector or a printed circuit board having a control circuit, to which the arrangement is connected.
As a solution to said problem the invention proposes an arrangement for measuring a fluid pressure according to claim 1.
In the arrangement the finding of the invention is brought to bear, namely that the portion with the pressure sensor is fashioned as a body having, in relation to its longitudinal axis, laterally protruding surfaces, wherein the sum of, relative to the longitudinal axis, orthogonal projections of surfaces, which are oriented substantially in a first direction and during operation are wetted by fluid, the pressure of which is to be measured, is substantially equal to, or less than, the sum of, relative to the longitudinal axis, orthogonal projections of surfaces, which are oriented substantially in a second direction opposite to the first direction and during operation are wetted by fluid, the pressure of which is to be measured.
The effect thereby achieved is that, given identical areas, during operation the portion with the pressure sensor is accommodated practically in a force, or pressure, balanced manner in the recess. In contrast to the apparatus described in previously described DE-GM 1 879 755, as pressure increases, the portion with the pressure sensor is not displaced. Given a slight imbalance in favour of the surfaces facing in the direction of the introduction side or introduction opening of the recess, the effect achieved is that, as pressure increases, the portion is pressed more and more firmly in the direction of the base of the recess. This increases the intrinsic reliability of the arrangement and is moreover an important difference from arrangements from prior art, in which an increasing fluid pressure usually has the tendency to push the pressure sensors as a rule out of their assembly bores.
Furthermore, the pressure sensor portion is easily insertable into the recess, thereby enabling short assembly times. Disassembly is also possible very quickly and easily because there are no snap rings retaining the pressure sensor portion. Rather, the pressure sensor portion is accommodated in the recess so as to slide in the sealing seat and may be removed from the recess or inserted into the recess without difficulty.
In particular, with the refinement according to the invention it is also easily possible, when a plurality of pressure sensors are provided in a hydraulic unit, for all of them to be mounted on the same printed circuit board before being attached simultaneously (as it were, in a stroke) to the hydraulic control unit.
In a preferred embodiment of the invention, first and second surfaces, which are situated on the pressure sensor portion and in contact with fluid, are so dimensioned and aligned that forces, which are exerted by the fluid pressure on the first surfaces and push the pressure sensor portion in the direction of the open end of the recess, are equal to the forces, which are exerted by the fluid pressure on the second surfaces and push the pressure sensor portion away from the open end of the recess. Thus, during operation of the pressure sensor the pressure sensor portion does not execute any movements in an axial direction. The pressure sensor portion may therefore be electrically and mechanically connected without difficulty to a printed circuit board for attachment to the hydraulic control unit, either by being directly soldered or welded thereon or contacted via a plug-in connection.
During operation no mechanical (tensile or thrust) loads are exerted by the pressure sensor portion on the electrical connection and/or the printed circuit board.
In a preferred manner the first surfaces and the second surfaces are, in relation to a centre plane, symmetrical to one another. This applies particularly when the pressure sensor portion comprises a circular cylindrical basic body, from which said first surfaces and second surfaces protrude radially or at a diametrically opposed angle (in relation to a plane at right angles to the central longitudinal axis).
In a currently preferred embodiment, the pressure sensor portion in a middle region has a first collar with a substantially closed lateral surface and a first end surface and a second end surface, and wherein the first end surface and the second end surface have substantially identical areas. Disposed at axial distances from the first and the second end surface of the first collar are a second and a third collar, the external dimensions of which are such that the second and the third collar help to guide the pressure sensor portion in the recess and have end surfaces, which each face the first collar and have substantially identical areas.
Disposed between the first collar and the second collar and/or between the first collar and the third collar there is in each case a seal.
The pressure sensor portion may additionally be secured in the recess by a retaining means, preferably a snap ring.
In a preferred manner the pressure sensor portion is so dimensioned and disposed in the recess that the first collar faces a fluid inlet disposed in the wall of the recess. In this case, it is not absolutely necessary for the pressure sensor portion in its mounted state to be situated xe2x80x9cat the same heightxe2x80x9d as the fluid inlet disposed in the wall of the recess. Rather, it should merely be ensured that, when fluid flows into the recess, the fluid does not first encounter one of the first or second surfaces. Thus, the fluid should reach the surfaces practically simultaneously so that the pressure sensor portion does not move in axial direction when the fluid flows in.
In an embodiment of the invention which is particularly easy to manufacture, the pressure sensor portion has a shape which is rotationally symmetrical relative to its central longitudinal axis.
The pressure sensor portion preferably has in the region of the first collar a pressure sensor. The pressure sensor may be a semiconductor pressure sensor.
With the invention it is also possible for ambient atmospheric pressure to prevail outside of the second and/or third collar. In other words, it is only between the second and the third collar that the pressure sensor portion is surrounded by pressurized fluid (the pressure of which is to be measured).
Regions of the pressure sensor portion lying axially further out, delimited by the second and/or third collar and/or the appropriate seals, may be situated in an unpressurized ambient atmosphere.
In a preferred embodiment, the pressure sensor portion and/or at least individual portions of the first, second or third collars have a cylindrical or conical, preferably circular cylindrical or circular conical shape.
The seals, which are disposed between the first collar and the second collar or between the first collar and the third collar, are preferably such that during operation they behave like an incompressible fluid when they are applied against the appropriate surfaces of the pressure sensor portion. It is thereby ensured that no corruption of the measurement occurs as a result of compliant seals. A further property of the seals should be that the regions of the seals, which are covered or wetted by the fluid during operation, are substantially diametrically opposed. Here, the same grounds and dimensioning rules apply as for the first and second surfaces of the pressure sensor portion.
The pressure sensor is therefore formed by a pressure sensor portion, which is surrounded in a fluid-tight manner by the wall of the recess, wherein the pressure sensor portion has two sealing elements (the second and third collars or appropriate seals), which have diametrically opposed sealing surfaces. The fluid, the pressure of which is to be measured, is introduced laterally into an inlet in the wall of the recess between the second and third collars or the appropriate seals.
Further properties, advantages, features and possible variants of the invention will become apparent to those skilled in the art from the following detailed description of a currently preferred embodiment of the invention, when read in light of the accompanying drawing.